This invention relates to the cooling of electronic equipment.
Electronic equipment conventionally comprises a housing containing electronic circuitry. In use, electronic components of such circuitry generate heat which, unless dissipated, may cause overheating of individual components, thereby resulting in their malfunction or complete breakdown. To remove this generated heat, a cooling air flow is introduced in which cooling air is forced past the circuitry including the electronic components. In a typical type of electronic equipment, the housing contains shelves each of which is provided with receiving stations to hold electronic circuitry units in side-by-side relationship. Each of such units comprises at least one printed circuit board carrying a plurality of electronic components which project into a cooling air flow passage between that particular printed circuit board and an adjacent board. Cooling air is introduced into the housing through an air inlet and is driven or drawn by fan devices through the cooling air flow passages between boards and then out from the housing through an air outlet. In this way, heat collected by the cooling air is expelled into the outside environment.
The above method of removing heat from electronic components has been generally satisfactory in the past. However, advancing technology is now enabling electronic circuitry to be designed in which conductors and electronic components are more densely positioned upon boards whereby greater quantities of heat are generated over set time periods by unitary areas of circuitry. Such rates of increase in heat generation require accompanying rates of increase in heat removal. One criteria for the rate of heat removal is the velocity of cooling air through the air flow passages. The conventional methods of producing cooling air flow have not been found particularly adequate in removing heat at required rates from electronic circuitry as the density of the circuitry, particularly the density of electronic components, increases. Should the flow rate for air be increased in an attempt to remove heat at the required increased rate, then increased resistance is found as provided at the inlet and outlet and by any air filter which is present. This obviously detracts from the requirement for increased air flow and places a limit upon the maximum air flow rate through the equipment.
The present invention seeks to provide a housing for electronic equipment and a method of passing cooling air through electronic equipment in a housing and which at least lessens the above problem.
According to the present invention, there is provided a housing for electronic equipment comprising:
an inlet into the housing for cooling air;
a cooling air flow passage system within the housing, the passage system comprising a first part of the system and a second part of the system connected to the first part at:
a) a first location downstream along the first part of the system from the inlet for the flow of cooling air from the first to the second part of the system; and
b) a second location upstream along the first part of the system from the first location for return flow to and recirculation of cooling air along the first part of the system; an outlet for expulsion from the system of cooling air containing heat; and
a device for generating a flow of cooling air through the inlet and through the passage.system and cause expulsion of a portion of the cooling air from the outlet and the simultaneous flow of the remainder of the cooling air from the second to the first part of the system to mix with cooling air entering through the inlet and flow along the first part of the system.
In use of housings according to the invention, there is an air exchange volumetric flow rate, i.e the rate at which cooling air is exhausted from the outlet and is replaced by fresh cooling air entering through the inlet. However, because of the recirculation design of the passage system, cooling air returns to the first part of the system from the second part to add to cooling air entering the system, whereby the volumetric flow rate of cooling air along the first part of the system must be greater than the volumetric flow rate of air entering the housing. As a result, for this volume of air to travel along the first part of the system, the air flow speed must be greater than in a housing structure having comparable inlet, outlet and cooling air flow generating device, while being devoid of a recirculation feature as in structures of the invention.
Hence, a structure of housing is made possible by the invention in which the air exchange volumetric flow rate is less that the volumetric flow rate through the first part of the system, thereby resulting in increased air flow speed past electronic components positioned in the first part of the system. The recirculatory arrangement thus enables the use of an acceptable and minimal size for the inlet and outlet, thereby maximizing the space available in the housing for electronic circuitry while increased air flow speed is also provided for cooling purpose. As a result, there is an increase in rate of heat removal from electronic components mounted within the first part of the system thereby allowing for increase in density of electronic components.
In a practical arrangement, the first and second parts of the passage system lie parallel with a barrier of the housing separating these parts, the barrier extending between the first and second locations in the housing. The barrier may conveniently comprise an interconnecting plane for electrically connecting electronic circuitry units in the first part of the system to other electronic circuitry units in the second part.
While the passage system may be oriented in any desirable fashion, conveniently it is ideally oriented with both the first and second passage parts extending vertically so that the interconnecting plane is also vertically disposed. In this arrangement, the inlet and outlet may conveniently be located one at an upper region of the housing and the other at a lower region, with preferably the inlet being at the upper region. In this latter case, the first location of interconnection of the first and second passage parts is disposed at the lower region whereas the second location is disposed at the upper region. At the lower region, the cooling air flow generating means may also be located. The generating means may, of course, be disposed in any other desirable position of the passage system. Also, either the inlet or outlet may be disposed in positions other than those mentioned above. For instance, with the inlet located at the upper region of the housing for flow of air downwardly along the first part of the system, the outlet may be disposed in a central or upper region of the second part of the system. In this case the total volume of air moving through the first part of the system and through the air flow generating device continues also along the second part of the system until it reaches the outlet. With this arrangement, some of the cooling air is expelled while the remainder continues along the second part of the system for recirculation into the first part.
With constructions according to the invention, the opening for air at either the inlet or outlet, or both, may be adjustable to vary the air exchange volumetric flow rate. Such adjustment would provide a resultant change in volumetric flow rates through different parts of the system.
The invention also includes a method of cooling electronic equipment comprising:
causing cooling air to flow through an inlet and along a first part of a passage system and between electronic circuitry units located within the first part of the system;
causing at least some of the cooling air to flow, at a first location, from the first part and into and along a second part of the passage system;
causing some of the cooling air to pass from the equipment out from an air outlet and, at a second location, causing some of the cooling air to return to the first part from the second part of the passage system; and
allowing the cooling air returning to the first part from the second part of the passage system to mix with cooling air entering through the inlet to provide a volumetric flow rate of air passing through the first part of the system which is greater than the volumetric flow rate of cooling air entering through the inlet.